The cutting and non-cutting links making up a saw chain of a power-driven chain saw are worn down because of use. The cutting links are, in addition, also worn away by repeated sharpening of the cutting edge and filing down of the depth limiter. The links of the chain such as the cutting links and the connecting links are also worn at the lower horizontal edges thereof as they move along the guide bar of the chain saw and are engaged by the drive sprocket thereof.
With known saw chains, the operator cannot accurately determine if the wear of the individual chain links, and hence of the entire chain, has reached the extent that operation of the power chain saw no longer is advisable because of excessive wear of the chain links. This is also true for saw chains wherein the cutting links are resharpened manually or by means of a sharpening device fastened on the power saw.
As a consequence of such wear, accidents repeatedly occur during work with known power-driven chain saws because of failure of the saw chains. Frequently this results from the fact that the operator applies increased advancing pressure to a dull chain, as a result of which great wear occurs along the underside of the cutting links, and in the extreme situation can lead to wearing away of the material down to the rivets which connect the chain links with each other. In such a case, the profile or section of the respective chain links is weakened all the way to the rivet bore so that cracks form which subsequently lead to failure of the chain.
The same disadvantage can arise due to depth limiters which are filed down to such an extent by the operator of the chain saw that it is at an elevation which is no longer safe for the cutting tooth associated therewith.
A further cause of chain failure is the wear caused by the chain drive sprocket, the teeth of which mesh in openings along the underside of the chain links, particularly the cutting links, and transmit the drive torque to these chain links. This is also true for the connecting links located adjacent the cutting links.
Additionally, injuries to the chain saw operator can occur if the remainder of the cutting teeth tear off where such teeth have been worn to the point where they have insufficient strength to withstand the cutting load applied thereto.